1. Field of the Invention
The present invention relates to an improvement in the structure of an optical switch for switching the optical path of an optical fiber.
2. Related Background Art
As is well known, an optical switch is an optical device for switching the optical path of an optical fiber along the time axis or spatially, and is widely utilized in the fields of optical communication, optical information, applied optical measurement, and the like.
The fields of optical communication, optical information, applied optical measurement, and the like have made remarkable developments in recent years. Along with these developments, an optical circuit has become more and more complicated and has advanced functions. Accordingly, further downsizing is demanded for an optical device.
Optical switches briefly described above are usually classified into mechanical type optical switches disclosed in, e.g., Japanese Patent Laid-Open Nos. 1-99016, 55-43540, and 55-25023, U.S. Pat. No. 5,056,886, and Japanese Patent Laid-Open Nos. 54-28160 and 2-149806, and non-mechanical type optical switches.
An optical switch disclosed in Japanese Patent Laid-Open No. 1-99016 has a mechanical structure in which a selecting connector is fitted to the distal end portion of a single optical fiber, and selected connectors are fitted to the distal end portions of a plurality of optical fibers arranged in a matrix.
The optical switch having the above arrangement has a function of arbitrarily selecting one connector selected from the plurality of connectors to be selected and thereafter moving the selecting connector in the X-, Y-, and Z-directions and fitting and connecting it to the one opposing connector to be selected, thereby switching the optical path of the optical fiber.
The optical switches disclosed in Japanese Patent Laid-Open Nos. 55-43540 and 55-25023, and U.S. Pat. No. 5,056,886 have a mechanical structure in which the optical path of a fiber is switched by using a mirror, a prism, and the like.
The optical switch disclosed in Japanese Patent Laid-Open No. 54-28160 is constituted by a single optical fiber which is bent due to use of an electrostrictive material, and a plurality of optical fibers disposed in a substantially fan-shaped manner and each having one end portion directed to the distal end portion of the opposing single optical fiber.
This optical switch has a function of arbitrarily selecting one optical fiber from the plurality of optical fibers, bending the single optical fiber with use of the electrostrictive material, and thereafter connecting the distal end portion of the single optical fiber to one end portion of the selected optical fiber, thereby switching the optical path.
Furthermore, an optical switch disclosed in Technology Research Report OCS 90-26 of the Institute of Electronics and Communication Engineers of Japan has a mechanical structure in which a magnetic film pipe is fixed to a bendable single optical fiber by adhesion, this single optical fiber is bent by a magnetic force, and this single optical fiber is aligned with one of a plurality of optical fibers by using a guide groove, thereby switching the optical path of the optical fiber.
Furthermore, an optical switch disclosed in Japanese Patent Laid-Open No. 2-149806 has a mechanical structure in which optical fibers are inserted in a plurality of adapters that are arranged in a line, one adapter is arbitrarily selected from the plurality of adapters, a semi-circularly arcuated single optical fiber is moved by rotating a ball screw, the distal end portion of the single optical fiber is inserted into the selected adapter, and the selected optical fiber and the single optical fiber are connected, thereby switching the optical path.
As a non-mechanical type optical switch, a waveguide type optical switch using a material, e.g., LiNbO.sub.3, a bulk type optical switch which deflects the optical path by using a liquid crystal or hologram, and the like exist.
Since the conventional optical switches have the above arrangements, they have several defects and problems as follows.
Since the optical switch disclosed in Japanese Patent Laid-Open No. 1-99016 utilizes selecting and selected connectors, a large fitting force must be applied to fit the connectors.
Accordingly, the housing of the switch must be formed of a strong material to maintain a large rigidity so that the housing can endure the fitting force. In addition, the switch becomes inevitably large.
In a detachable-connector optical switch of this type, the end face of the optical fiber can be polished for each connector to decrease reflection at the coupling portion. However, since the connectors must be connected to and disconnected from each other, an increase in size cannot be avoided.
In the optical switches disclosed in Japanese Patent Laid-Open Nos. 55-43540 and 55-25023 and U.S. Pat. No. 5,056,886, since alignment of the optical fiber requires high precision, an expensive, high-grade positioning mechanism must be provided as an actuator. The assembly operability of the system cannot be improved, and the system is very weak against vibration and the like, thus lacking reliability.
In the optical switch disclosed in Technology Research Report OCS 90-26 of the Institute of Electronics and Communication Engineers of Japan, although the positioning precision of the actuator can be coarse, the optical switch cannot be directly applied to and utilized at all in a multi-core structure having three or more cores.
In the optical switch disclosed in Japanese Patent Laid-Open No. 2-149806, the plurality of optical fibers must be arranged highly precisely.
Furthermore, the non-mechanical optical switches described above have problems of a large loss, large crosstalk, large polarization dependency or wavelength dependency, and the like that cannot be neglected in terms of reliability.
Meanwhile, in addition to the above defects described in detail, the conventional optical switches require a sensor for position detection. When this sensor is housed in the switch, problems arise, e.g., the size is increased, the electric wiring is complicated, and the cost is increased.
Since a mechanism (nonvolatile function) for stably maintaining coupling when power is not supplied is added to the conventional optical switches, an increase in size cannot be avoided.